Shaft seal

ABSTRACT

A rotary shaft seal is characterized by a buffer compartment filled with fluid maintained at a pressure which equals or exceeds the pressures along the shaft with which the seal is associated. The relatively high buffer pressure within the seal is effective to prevent passage of material along the shaft from one side of the seal to the other. In one preferred embodiment, the device for applying pressure to the buffer fluid within the compartment is responsive to the pressures along the shaft adjacent to opposite sides of the seal. The intensity of pressure applied to fluid within the buffer compartment is a function of the pressures along the shaft. This preferred embodiment is an effective driveshaft seal for the expander in a Rankine cycle engine, wherein the pressure applying device responds to both the pressure within the expander and the pressure outside the expander and applies to fluid in the buffer compartment a pressure higher than either of them.

United States Patent 1 Doyle et al.

[ SHAFT SEAL Inventors: Edward F. Doyle, Dedham; Thomas LeFeuvre,Woburn, both of Mass.

[73] Assignee: Thermo Electron Corporation,

Waltham, Mass.

Filed: May 28, 1971 Appl. No.: 148,027

[52] US. Cl. 277/3, 60/36, 417/901,

Int. Cl F16] 15/00 Field of Search 277/3, 12, 17, 27,

References Cited UNITED STATES PATENTS 12/1940 La Hour 277/62 8/1966Richards 277/70 Primary ExaminerSamuel B. Rothberg AssistantExaminer-Robert 1. Smith Attorney-James L. Neal 11 June 19, 1973ABSTRACT A rotary shaft seal is characterized by a buffer compartmentfilled with fluid maintained at a pressure which equals or exceeds thepressures along the shaft with which the seal is associated. Therelatively high buffer pressure within the seal is effective to preventpassage of material along the shaft from one side of the seal to theother.

within the expander and the pressure outside the expander and applies tofluid in the buffer compartment a pressure higher than either of them.

22 Claims, 10 Drawing Figures Pmmnnw 3.740.057

SHEEN 0F 5 62 68 FIG.I

INVENTORS EDWARD DOY BY THOMAS FIEU ATTORNEY PArimzn 5.740.057

SHEET I 0F 5 Fl 6. a

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- INVENTORS EDWARD F. DOYLE THOMAS LEFEUVRE BY ATTORN EY Pmmwwm5.140.057

SHEET 5 0F 5 F lG.9

INVENTORS EDWARD F. DOYLE THOMAS LEFEUVRE BY J fi ATTORNEY SHAFT SEALBACKGROUND OF THE INVENTION The passage of a rotary shaft through thecasing of a driving or driven apparatus is attended by a sealing problemwhich is particularly difficult when the pressures within or surroundingthe casing are subject to significant variation so that first one andthen the other of the pressures is higher. A highly effective seal isrequired to prevent passage of the material from the surroundings intothe casing and to prevent passage of the material from the easing intothe surroundings.

One situation involving the problem outlined above is presented by thedriveshaft of an expander in a Rankine cycle engine. Typically, a rotarydriveshaft passes through the expander casing and engages the device tobe driven. During operation of the engine, pressure within the expandercasing fluctuates over a wide range extending above and below thepressure surrounding the casing, which is typically the ambientatmosphere. During extended periods of non-operation, the pressure inthe casing falls to a substantially subatmospheric level due in part tothe cooling attending shut-down of the engine. It is essential toprevent passage of fluid within the expander into the atmosphere and toprevent the passage of air into the expander.

Fluids contained within the expander casing include a lubricant,orlubricants, and the working fluid for the Rankine cycle engine. Bothfluids are present at the location where the shaft passes through theexpander casing. Typically, the working fluid is sufficiently expensivethat its conservation becomes an extremely important matter in efficientoperation of the Rankine cycle engine. Further, a pre-determined optimumamount of working fluid must be maintained within the system to enableit to operate at peak efficiency. When the pressure in the casing isabove atmospheric pressure, fluids in the casing continually tend to beforced out into the atmosphere along the driveshaft. Loss of thesefluids is accompanied by a substantial reduction in operating efflciencyand a substantial increase in operating expense.

It is also of primary importance in Rankine cycle systems that materialin the surrounding environment be kept out of the expander casing.Foreign material entering the casing is distributed throughout thesystem to the detriment of system performance. Thesurroundingenvironment, as pointed out above, is typically the ambient atmosphere.Entry of air into the engine is particularly deleterious to systemperformance. This detriment apparently results from nitrogen and oxygen,which constitute the major gases in the atmosphere. Nitrogen collects inthe condenser of the system and substantially reduces the operatingefficiency of the condenser and thereby of the system. Oxygen, in thepresence of the working fluid' and lubricant, accelerates their rates ofthermal decomposition and, accordingly, substantially increases theexpense required to operate the system.

SUMMARY OF THE INVENTION The present invention relates to a seal forpreventing movement of material either into or out of a casing along arotary shaft. The sealing elements include a first means mounted on theshaft forming a first pair of sealing surface areas and a second meansmounted on the casing forming a second pair of sealing surface areas insealing engagement with the first sealing surface areas. A buffer fluidchamber containing pressurized buffer fluid surrounds the sealingelements. Buffer fluid pressure is maintained sufficiently high that thetendency of buffer fluid to pass between the sealing surfaces at leastequals the tendency of material to pass between the sealing surfacesfrom either inside or outside of the casing. Thereby, passage ofmaterial past the sealing surface areas either into or out of the casingis effectively prevented.

Small amounts of the buffer fluid may pass the sealing surfaces andenter the casing or the environment surrounding the casing. Accordingly,the buffer fluid is selected so as not to be harmful to material withinthe casing or harmful when present in the environment. The buffer fluidmay be a suitable lubricating fluid.

The seal is particularly effective when used on the expander driveshaftin a sealed Rankine cycle engine. To prevent passage of the fluid fromthe expander casing along the driveshaft into the atmosphere and toprevent passage of the atmosphere into the expander casing, the bufferfluid pressure is constantly maintained at a pressure level equaling orabove both atmospheric pressure and any anticipated crankcase pressure.In a preferred embodiment of this invention, the buffer fluid pressureis maintained at the desired level by apparatus responsive to bothatmospheric pressure and the pressure within the expander casing.

It is a primary object of this invention to provide a rotary shaft sealwhich prevents passage of material in either direction along a shaftpast the seal.

It is a further object of this invention to provide a rotary shaft sealwhich prevents passage of material in either direction along a shaftpast the seal wherein the seal is responsive to pressures surroundingthe shaft on opposite sides thereof for maintaining within the seal abuffer pressure which equals or exceeds the pressures surrounding theshaft.

It is also an object of this invention to provide a rotary shaft sealfor the expander of a Rankine cycle engine which prevents passage offluids from the expander tothe atmosphere and from the atmosphere intothe expander.

A further object of this invention is to provide a rotaryshaft seal forthe expander of a Rankine cycle engine which is responsive to both thepressure within the expander and atmospheric pressure for maintainingwithin the seal a buffer pressure which equals or exceeds both thepressure within the expander and the atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a preferredembodiment of the rotary shaft seal of this invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 illustrates an alternate embodiment of the apparatus shown inFIG. 2;

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 1;

FIG. 5 presents an alternate embodiment of the rotary shaft seal shownin FIG. 1;

FIG. 6 illustrates an alternate embodiment of the apparatus shown inFIG. 4;

FIG. 7 illustrates another alternate embodiment of the apparatus shownin FIG. 4;

FIG. 8 is a schematic view of a Rankine cycle system according to thisinvention;

FIG. 9 is a sectional view of a reciprocating piston expanderconstructed according to this invention; and

FIG. 10 is a schematic view showing a turbine expander constructedaccording to this invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIG. 1, a rotary shaft10, to which a driven member 8 is attachable, extends through a casing12, the casing being comprised of parts 14 and 16. A structure 11establishes a seal between the shaft and the casing.

The sealing structure 11 includes a first sealing element in the formofa ring 18 and a pair of sealing elements 26 and 26'. The sealing ring18 is affixed to shaft 10 near an outer portion of the casing 12. Thesealing ring 18 may be formed of any suitable material such as hardenedsteel, cast iron or the like. Mounted on the casing 12 are substantiallyidentical sealing elements 26 and 26', each of which sealing engages aseparate sealing area of the sealing ring 18, as will be more fullydescribed below. The interface between the sealing ring 18 and thedriveshaft 10 is sealed hermetically by static O-ring seal 20. Theinterface between the the casing 12 and the sealing elements 26 and 26is provided with hermetic O-ring seals 27 and 27'.

Since the sealing elements 26 and 26 are substantially identical, onlysealing element 26 will be described. In sealing element 26', likeprimed numerals designate like parts.

The sealing element 26 comprises an outer enclosure 28 supporting asealing ring 30 of suitable material such as carbon, an O-ring 32,spring means 34, means 36 for confining the O-ring 32, and means 38 forconfining the carbon sealing ring 30. The carbon sealing ring 30 ispositioned for direct engagement with the sealing ring 18 and is pressedinto continuous firm sealing engagement by the spring means 34. TheO-ring 32 establishes a static seal between the carbon sealing ring 30and the enclosure 28 to prevent passage of material between the carbonsealing ring and the enclosure. The means 36 maintains the O-ring inproper sealing engagement with the carbon sealing ring and the enclosure28. The means 38 confines the carbon sealing ring 30 to maintain it infixed position relative to the enclosure 28, thereby avoiding movementof the carbon sealing ring 30 relative to the shaft 10 when the shaft 10and the mating ring 18 rotate. The means 38 may engage the carbonsealing ring 30 in a detent, not shown, or in any other suitable manner.

The elements 18, 26 and 26' of the sealing structure .11 are mountedadjacent the journal box where the driveshaft 10 passes through thecasing 12. The sealing ring 18 is firmly pressed against a shoulder 22of the driveshaft by a threaded retaining member 24. The sealing element26 abuts a journal bearing 40. The bearing face 42 of the carbon sealingring 30 associated with the sealing element 26 is positioned in sealingengagement with one surface area of the sealing ring 18. The sealingelement 26 is positioned so that its bearing surface 42' sealinglyengages an opposite surface area of the sealing ring'l8. The sealingelement 26 is firmly secured in position by a retaining ring 44.

Surrounding the points of sealing engagement between the sealingelements 26, 26 and 18 is a compartment 48 for containing a bufferfluid. The compartment is so formed that buffer fluid contained thereinwill be continuously present at the interface between the sealing ring18 and the sealing rings 30 and 30.

When the driveshaft 10 is rotated, heat is generated due to thefrictional engagement between the sealing ring 18 and the carbon sealingrings 30 and 30. This heat builds up in the buffer fluid within thecompartment 48. Accordingly, a method of circulating and cooling thebuffer fluid is required. The amount of heat generated is such that thebuffer fluid temperature may be maintained at the proper level bycirculation of the buffer fluid through a closed cooling loop 55. Thecool ing loop is formed by lines 50 and 54 which lead from buffer fluidoutlet 52 and buffer fluid inlet 56, respectively, and are connected bycoupling 58. Circulation of the buffer fluid may be produced by anyconvenient means. For example, apumpingstructure may be included withinthe sealing structure 11 or a pump, not shown, may be installed alongthe closed loop 55.

In FIG. 1, pumping action is produced by cooperation between the sealingelement 18 and the buffer fluid compartment 48 in a manner which is bestdescribed with reference to FIG. 2. The buffer fluid compartment 48 isformed eccentrically within the casing 12 so that the central axes ofthe sealing ring 18 and of the buffer fluid compartment 48 do notcoincide. When heat is generated by frictional engagement between thesealing elements, the sealing ring 18 acts as an impeller within thecompartment 48 to build a relatively high pressure adjacent the outlet52 and a relatively low pressure adjacent the inlet 56. The smallpressure differential created in this manner is enough to establish therequired flowof buffer fluid through the loop 55. The heat exchangewhich takes place along the lines forming the loop is sufficient tomaintain the temperature of the buffer fluid at the appropriate level.

An alternate embodiment of buffer fluid pump is illustrated in FIG. 3.In this embodiment, the sealing ring 18 and the buffer fluid compartment48 are concentri- 'cally formed within the casing 10. The sealing ring18 has formed thereon a series of vanes 60 which serve as impellers tobuild a pressure differential between the inlet 56 and the outlet 52.

For the sealing structure 11 to prevent passage of fluid or othermaterial in either direction along the driveshaft 10 under any and allcircumstances, the pressure of the buffer fluid must constantly bemaintained at a level equal to or higher than the pressure surroundingthe shaft at opposite sides of the sealing elements 26 and 26.

To provide the required buffer fluid pressure, there is provided apressure source 62 joined by a connecting line 64 to the loop 55. Thepressure source 62 may operate in a number of ways to maintain therequired pressure level in the buffer fluid compartment 48. Onepreferred embodiment is illustrated in FIGS. 1 and 4. A housing 65comprises support means 66, a first end section 68 and a second endsection 70..Formed within the housing 65 is a hermetically sealed bufferfluid reservoir 72. The reservoir 72 is defined by a first flexiblediaphragm means 74 and a second flexible diaphragm means 76. Theflexible diaphragm means 74 and 76 include within their central portionrigid plates 78 and 80, respectively. A buffer fluid level indicator 108bearing indicia 109 extends from plate 78 through chamber 84. Within thereservoir 72 is established a port 82 which communicates with theconnecting line 64. Adjacent one side of the reservoir is a firstpressure chamber 84 formed by first end section 68; adjacent the otherside of the reservoir is a second pressure chamber 86 formed by thesecond end section 70. A compression spring 88 is interposed betweenplate 78 and surface 90 of the first end section 68. lnterposed betweenthe plate 80 and surface 94 of the second end section 70 is acompression spring 92. The springs constantly exert pressure on theplates and thus on the buffer fluid within the reservoir 72. Inaddition, pressure is applied to the buffer fluid within the reservoir72 by pressure within the pressure chambers 84 and 86. The additionalpressure applied to the buffer fluid is substantially equivalent toeither the pressure in the first pressure chamber 84 or the secondpressure chamber 86, as will be explained in more detail below. Withinthe first pressure chamber 84 is a stop 96 for limiting movement of theplate 78; within the second pressure chamber 86 is a stop 98 forlimiting movement of the plate 80.

The first and second pressure chambers are provided for applyingpressure to the buffer fluid in response to the pressure surrounding thedriveshaft on opposite sides of the sealing elements 26 and 26'. In theembodiment of FIG. 1, for example, the sealing element 26' is exposed toa zone of pressure outsidethe casing 12 and the sealing element 26 isexposed to pressure inside the casing 12. Accordingly, the firstpressure chamber 84 is constructed to respond to pressure outside thecasing by direct communication through ports 100 and 102. Also, a line104 extends from the second pressure chamber 86 to the interior of thecasing 12 to enable the second pressure chamber to respond to pressurewithin the casing '12.

Operation of the sealing structure 11 depicted in FIGS. 1, 2 and 4 willnow be described. The sealing structure prohibits communication betweenthefirst pressure zone on one side of the sealing elements 26 and 26'and a second pressure zone on the opposite side of these sealingelements, regardless of pressurefluctuations or of which pressure ishigher than the other. The buffer fluid chamber 48, the loop .55, theline 64, and the reservoir 72 are all filled with buffer fluid. Thepressure applied to the reservoir 72 by the springs 88 and 92 istransmitted to the'buffer fluid within the compartment 48 by means ofthe line 64 and the loop 55. The springs thus constitute a pressuresource constantly acting on the buffer fluid.

The first pressure chamber 84 is at a first pressurelevel correspondingto the pressure level outside the casing 12 and the second pressurechamber 86 is at the pressure level of the interior of the casing. Apressure equivalent to the higher pressure of the pressures within thechambers 84 and 86 is applied to the reservoir 72, in addition to thepressure applied to the reservoir by opposed springs 88 and 92. That is,when pressure in the second pressure chamber 86 exceeds pressure in thefirst chamber 84, the first and second flexible diaphragm means 74 and76 flex so that the reservoir 72 advances toward the stop 96 until thestop is abutted by the plate 78. The springs continue to act upon thereservoir while a force equivalent to the pressure in the secondpressure chamber 86 is applied thereto.Conversely, when pressure in thefirst pressure chamber 84 exceeds the pressure in the second pressurechamber 86, the first and second flexible diaphragm means flex to permitthe reservoir 72 to advance toward the stop 98 until this stop isabutted by the plate 80. In this condition, pressure substantiallyequivalent to the relatively high pressure in the chamber 84 is appliedto the buffer fluid in addition to the pressure applied thereto by thesprings.

The springs 88 and 92 are preferably calibrated so that pressure on thebuffer fluid within the compartment 48 always exceeds pressuressurrounding sealing elements 26 and 26'. However, the springs may becalibrated to apply a minimum force effective only to overcome anyfrictional resistance within the pressure source 62 or eliminatedentirely. In the latter event, the buffer fluid pressure willsubstantially equal the highest of the pressures surrounding the sealingelements 26 and 26. Since the pressure across the sealing faces ofelements 18, 26 and 26 is always characterized by either equilibrium orrelatively high buffer fluid pressure, there is never a tendency formaterial to pass along the shaft 10 from one side of the sealingelements 26 and 26' to the other side of these sealing elements.

There is a tendency for a small amount of buffer fluid to pass betweenthe sealing faces of the sealing ring 18 and the carbon sealing rings 30and 30. In event of passage, a small portion of the buffer fluid may belost either to one side or the other of the sealing elements 26 and 26'.Fluid which passes from the buffer fluid compartment 48 is replenishedfrom the reservoir 72. As the fluid is exhausted from the reservoir,flexible diaphragm means 74 and 76 advance toward each other to reducereservoir volume. The reservoir may or may not need periodic rechargingof buffer fluid depending on the life of the system within which thesealing structure 11 is used. Within the practical limits of reservoirsize, the supply of buffer fluid has been found sufficient for extendedperiods.

The sealing structure 11 operates in the manner described, whether ornot the driveshaft 10 is rotating within the casing 12, and is thereforeequally effective when the system in which it is used is operating andwhen the system is not operating.

The amount of buffer fluid in reservoir 72 at any given time is measuredby reading indicia 109 on the buffer fluid indicator means 108 withrespect to a reference point, such as the surface of housing 65. Toobtain a reading, the indicator means 108 must be in the fully advancedposition so that the plate 80 abuts the stop 98. In this position, theindicia 109 provides a reading of the distance between the plates 78 and80 and therefore of the volume of fluid within the reservoir 72. Whenthe pressure in the chamber 84 exceeds the pressure in the chamber 86,the plate 80 will be caused to I abut the stop 98 so that the positionof the indicator 108 inherently provides a reading of the reservoircontents. Further advancement of the indicator means 108 is prohibitedby the resistance of the stop 98 and the buffer fluid within thereservoir 72. When the pressure in the chamber 86 exceeds that in thechamber 84 (the condition shown in FIG. 4), the indicator means isadvanced against a resistance level which is a function of the pressuredifferential between the two pressure chambers. When a second resistancelevel resulting from engagement of the plate with the stop 98 isencountered, the indicator means 108 is fully advanced and a reading maybe taken.

Various alternate embodiments of the sealing structure 11 will now bedescribed. Like numerals will be used to designate like parts.

formed a buffer fluid chamber 112 eccentric with respect to thelongitudinal axis of the driveshaft 10. Mounted on the driveshaft 10 area pair of assemblies 114 biased away from each other into engagementwith the sealing rings 110 by a compression spring 116. Each of theassemblies 114 comprises a means 118 which provides a static sealbetween the shaft 10 and the assemblies 114 and positions a rotarycarbon sealing ring 120 in sealing engagement with the static sealingring 110. O-rings 122, 124, 126 and 128 hennetically seal the bufferfluid chamber 112 from the zones of pressure present along thedriveshaft 10. Inlet 56 and outlet 52 are provided to connect thechamber 112 with the pressure source 62, in the manner described abovein connection with FIGS. 1, 2 and 4. It will be appreciated that theembodiment of FIG. 5 operates substantially in the same manner as theone described in connection with FIGS. 1, 2 and 4 except that the staticsealing elements are mounted on the casing 12 and rotary sealingelements are mounted on the driveshaft 10.

In connection with FIGS. 6 and 7, there will be described two otherembodiments of the sealing structure 11 primarily involving the pressuresource 62. FIG. 6 shows one embodiment of pressure source 62 forapplying force to the buffer fluid independent of pressures surroundingthe driveshaft 10. A housing 65 is provided with a flexible bellowsdiaphragm 140 which divides the interior of the housing 65 into a bufferfluid reservoir 142 and a pressure chamber 144. The housing 65 isprovided with a port 82,for connection to the line 64 to establishcommunication with the loop 65. There is further provided a port 146 forthe admission of compressed gas into the pressure chamber 144.Compressed gas admitted through port 146 fills the pressure chamber 144to provide sufficient pressure on buffer fluid within the buffer fluidreservoir 142 to maintain the buffer fluid within the buffer fluidcompartment '148, shown in FIG. 1, at a level which equals or exceedsthe pressures surrounding the driveshaft 10 on opposite sides of theelements 26 and 26. The pressure applied to the reservoir 142 by thesource of compressed gas is calibrated to always provide at least theminimum pressure required for compartment 148.

The pressure source 62 shown in FIG. 7 includes a housing 65 dividedinto three sections by a first flexible diaphragm means 150 and a secondflexible diaphragm 152. The flexible diaphragm means 150 and 152 providehermetic sealing between the three sections of the interior of thehousing 65.

A chamber 154'is provided with ports 156 which establish communicationwith one pressure zone. A chamber 158 communicates through line 104 withanother pressure zone. A buffer fluid reservoir 160 communicates througha port 82 and the line 64 with the loop 55 and thence with thecompartment 48. The diaphragm means 150 includes a rigid plate-likestructure 162. From structure 162, a sleeve 164 projects into chamber158 and a projection 164 extends through the chamber 154. The projection164 forms a fluid level indicator. Indicia 166 thereon serves toindicate the amount of fluid present within the buffer fluid reservoir160. The diaphragm means 152 includes a second plate-like structure 168from which projection 170 extends upward into the chamber 158 andtelescopes within the sleeve 164. A retaining means 172 is mountedwithin the chamber 158. Opposed between the retaining means 172 and thestructure 168 is a compression spring 174.

The spring 174 continuously applies pressure to buffer fluid within thereservoir 160 and thus to fluid within the compartment 48. When thepressure in the chamber 158 is greater than the pressure in the chamber154, the diaphragms and 152 are urged apart from each other. (Thediaphragm 150, as shown in FIG. 7, is in the transitory state, movingaway from the diaphragm 152.) The diaphragm 150 advances to thepartition 176 and the diaphragm 152 is pressed firmly against bufferfluid in the reservoir 160. Under this condition, the pressure of thefluid within the chamber 158 is imparted to buffer fluid within thereservoir in addition to the pressure applied thereto by the spring 174.When the pressure within the chamber 154 exceeds that within the chamber158, the diaphragm 150 advances toward the diaphragm 152. Thisadvancement continues until the terminal portion 178 of the sleeve 164engages the terminal portion 180 of the projection 170. When thisoccurs, the projection and the sleeve are effectively coupled togetherso that pressure within the chamber 154 is applied to buffer fluidwithin the reservoir 160 in addition to pressure applied thereto by thespring 174.

The fluid level indicating means 164 provides for the determination ofthe amount of buffer fluid within the reservoir 160. When the pressurein chamber 154 exceeds that in chamber 158, the diaphragms areeffectively coupled as described above, and the indicia 166 on theprojection 164 will indicate the amount of fluid within the reservoir160. In this circumstance, the projection 154 will not be susceptible offurther downward movement into the housing 65. When the pressure inchamber 168 exceeds that in chamber 154, the diaphragm 150 will bepressed against the member 176 and the indicia 166 on the projection 164will indicate that the reservoir is full. When the reservoir isindicated full, to determine that this is actually a correct reading,the projection 164 must be pressed inwardly of the housing 165, againstthe force applied thereto by the pressure differential between thechambers 158 and 154, until a second level of resistance is encounteredbeyond which the projection is no longer movable. The reading at thesecond level of resistance is the correct indication of the amount offluid within the reservoir 160. If upon pressing the projection 164inwardly on the housing 165, it is immediately immovable, the reservoir160 is full of buffer fluid.

Turning now to FIGS. 8 and 9, there will be described a Rankine cyclesystem constructed according to this invention to prevent passage of thefluid from the system into the atmosphere and passage of material fromthe atmosphere into the system.

The Rankine cycle system is described briefly in connection with FIG. 8.A vapor generator 182 heats organic working fluid fed thereto by a pump184. The vaporized working fluid is then directed to an expander 186which expands the vapor through a substantial temperature and pressuredrop to produce work and rotate the driveshaft 10. The working fluidthen passes from the expander 186 through a separator 188 which removesany lubricants from the organic working fluid,

which lubricants are returned to the expander by a line 190. The workingfluid then enters the vapor side 192 of a regenerator 194 and gives upsome of the heat energy remaining therein to working fluid passingthrough the liquid side 196 of the regenerator. From the vapor side 192of the regenerator, the working fluid passes through the condenser 198and is fully condensed. The pump 184 then drives the condensed workingfluid through the liquid side 196 of the regenerator 194 and back to thevapor generator 182. The working fluid is heated as it is driven throughthe liquid side of the regenerator by exhaust vapor passing through thevapor side of the regenerator. The vapor generator 182 vaporizes theworking fluid and the cycle is repeated.

FIG. 9 illustrates a reciprocating expander for a Rankine cycle systemof the type shown in FIG. 8. The expander is provided with a casing 200comprising parts 202 and 204. Within the casing 200 is a vapor inletmanifold 206 and valves 208 and 210 cooperatively arranged with respectto reciprocatingpistons 212 and 214. Each of the pistons have associatedtherewith a When the Rankine cycle expander is operating and ments 26and 26', it is replenished from the reservoir piston rod 216 and 218.The piston rods are connected to a crankshaft 220 which is supportedwithin the casing 200 at one end by a journal box 222. A driveshaft 10extends from the opposite end of the crankshaft and is supported in thecasing 200 by a journal box 224. Adjacent the journal box 224 aresealing elements 18, 26 and 26' surrounded by a buffer fluid compartment48. The sealing elements, compartment and other associated parts areconstructed and mounted in substantially the same fashion as describedabove in connection with FIG. 1. Lines 50 and 54 extend from thecompartment 48 to form the loop 55 which is connected by line 64 to thepressure source 62. Extending from the pressure source 62 is a line 104establishing communication between pressure source and the interior ofthe casing 200. The line 104 should enter the casing 200 at a placerelatively near the journal 224 so that it may enable the pressuresource 62 to accurately sense the pressure adjacent the sealing element26.

The operation of the apparatus of FIG. 9 will now be described inconnection with the buffer fluid compartment as shown in FIG. 2 and thepressure source as shown in FIG. 4.

The expander 186 is characterized by wide variations of internalpressures. The pressure in the casing 200 may extend to levels wellabove atmospheric pressure under certain conditions and, under otherconditions, drop substantially below atmospheric pressure. Consequently,the shaft seal is required to prevent passage of material from withinthe casing to the atmosphere when the casing pressure is relatively highand to prevent passage of material from the atmosphere into the casingwhen the casing pressure is relatively low.

Vaporized working fluid admitted into the inlet manifold 206 from thevapor generator 182 is alternately directed first into cylinder 211 andthen into cylinder 213 by valves 208 and 210, respectively, in a typicalmanner understood in the art. Working fluid is exhausted from thecylinders through exhaust ports of the type.

shown at 215 in the cylinder 211. Alternate reciprocation of the pistons212 and 214 results from the admission into the cylinders 211 and 213and exhaust therefrom of vaporized working fluid. Reciprocation of thepistons rotates the crankshaft 220 which in turn causes the driveshaft10 to rotate within the casing 200.

72. During operation, when the pressure in the casing 200 exceedsatmospheric pressure, the casing pressure is transmitted through line104 to the second pressure chamber 86 of the pressure source 62. Thispressure is then applied by the pressure source 62 to the buffer fluidsystem. There is also applied to the buffer fluid system the pressureresulting from compression springs 88 and 92. The result is that thepressure of the buffer fluid within the buffer fluid compartment 48 isequal to the pressure in the casing 200 plus the pressure from thecompression springs 88 and 92. On the other hand, during long periods ofshut-down of the Rankine cycle system, the pressure within the casing200 typically drops below atmospheric pressure. Under this circumstance,the first pressure chamber 84 which communicates with the atmosphere bymeans of ports 100 and 102 is subjected to a relatively [high pressurewhich overcomes the influence of the pressure within the second pressurechamber 86. The atmospheric pressure is then applied to the buffer fluidsystem together with the pressure of compression springs 88 and 92 sothat buffer fluidwithin the buffer fluid compartment 48 is subjected toa pressure equal to the atmospheric pressure plus the pressure appliedby the compression springs.

Expanders are characterized by sealing arrangements between the pistonsand cylinders which permit passage of working fluid past the pistons andcylinders into the portion of the expander casing which containslubricant, with the result that working fluid becomes intermixed withthe lubricant. The tendency of material to pass from the interior of theepxander to the exterior thereof along the driveshaft establishes thepotential loss of both working fluid and lubricant. For example, in theexpander 186 of FIG. 9, working fluid tends to pass between thecooperating piston and cylinder assemblies to the portion 201 of thecasing 200 which serves as a lubricant containing crankcase. Thecrankcase 201 thus contains a mixture of lubricant and working fluidwhich passes through the journal 224 and would tend to pass between thesealing element 18 and sealing elements 26 and 26' except for thepressure of buffer fluid within the compartment 48.

FIG. 10 is a schematic view showing a turbine 300 embodying thisinvention. The sealing structure 11 is interposed between the casing ofthe turbine 300 and its driveshaft 10 to prevent passage of materialfrom one side of the sealing structure to the other along thedriveshaft. It should be understood that this invention is not limitedto expanders but may be' used on pumps and other apparatus wherein aneffective shaft seal is required.

This invention has been described by several preferred embodiments. Itwill be apparent that modifications and changes may be made withoutdeparting from 'the scope of the invention as set forth in the followinga first pressure zone on one side thereof and a second pressure zone onthe other side thereof, said shaft seal comprising:

a. first sealing means mounted in fixed relationship to said shaft meansand forming first and second sealing surface areas each surrounding saidshaft means;

b. second sealing means mounted in fixed relationship to said casingwall means and forming first and second sealing surface areas, saidfirst and second surface areas formed by said second sealing meansmating in sealing engagement with said first and second sealing surfaceareas of said first sealing means, respectively;

c. means forming a buffer fluid compartment communicating with saidfirst and second sealing means at their points of sealing engagement;

d. first means communicating with said first pressure zone;

e. second means communicating with said second pressure zone; and

f. means responsive to said first and second communicating means forapplying to buffer fluid within said compartment a pressure which atleast substantially equals the greater of the pressures in said firstand second pressure zones, thereby to inhibit passage of material alongsaid shaft means from either of said pressure zones to the other.

2. A shaft seal according to claim 1 wherein said pressure applyingmeans is responsive to the pressures in both said first and secondpressure zones.

3. A shaft seal according to claim 1 wherein said pressure applyingmeans comprises:

a. means forming a hermetically sealed expansible chamber communicatingwith said buffer fluid compartment; and

b. means responsive to both the pressure in said first pressure zone andthe pressure in said second pressure zone for applying to saidexpansible chamber and thereby to said compartment a pressure at leastsubstantially equaling the greater of either the pressure in said firstpressure zone or the pressure in said second pressure zone.

4. A shaft seal according to claim 3 wherein said pressure applyingmeans further comprises means for constantly applying pressure to saidexpansible chamber and thereby to said compartment in addition to thepressure applied thereto by said means responsive to the pressures insaid first'and second pressure zones, whereby the pressure applied tosaid compartment exceeds the greater of either the pressure in saidfirst pressure zone or'the pressure in said second pressure zone.

5. A shaft seal according to claim 3 wherein said expansible chambercomprises a buffer fluid reservoir.

6. A shaft seal according to claim 1 wherein said means responsive tosaid first and second communicating means is'in hermetically sealedfluid connection with said buffer fluid compartment.

7. In a Rankine cycle system including an expander having means forminga working fluid chamber and a rotary shaft extending from said workingfluid chamber into an environmental zone, wherein the pressure in saidworking fluid chamber rises above environmental zone pressure duringcertain conditions and drops below environmental zone pressure duringcertain other conditions, a shaft seal comprising:

a. a first sealing means on said shaft in fixed, fluid tightrelationship thereto and having first and second sealing surface areassurrounding said shaft;

b. second sealing means in fixed, fluid tight relationship to said meansforming said working fluid chamber and having first and second sealingsurface areas in sealing engagement with said first and second sealingsurface areas, respectively, of said first sealing means;

0. means forming a buffer fluid compartment in communication with saidfirst and second sealing means at their points of engagement formaintaining a supply of buffer fluid at said points of engagement; and

d. means in hermetically sealed fluid communication with saidcompartment constantly applying pressure to buffer fluid therein whichat least equals the greater of either the pressure in said working fluidchamber or the pressure in said environmental zone, said pressure beingapplied during both operating and non-operating conditions of theRankine cycle system, thereby to eliminate the tendency of material topass along said shaft from said working fluid chamber into saidenvironmental zone when pressure in said working fluid chamber is aboveenvironmental zone pressure and from said environmental zone into saidworking fluid chamber when pressure in said working fluid chamber isbelow environmental zone pressure.

8. In a Rankine cycle system according to claim 7 a shaft seal whereinsaid pressure applying means applies to buffer fluid within saidcompartment a pressure greater than either the pressure of said workingfluid chamber or the pressure of said environmental zone.

9. In a Rankine cycle system according to claim 7 a shaft seal wherein:

a. said first sealing means comprises an annular flange surrounding saidrotary shaft;

b. said second sealing means comprises a pair of annular sealingsurfaces for sealing engagement with opposite sides of saidannularflange; and

c. said buffer fluid compartment surrounds said annular flange along andbetween the points of engagement of said annular flange with said pairof annular sealing surfaces.

10. In a Rankine cycle system according to claim 9 a shaft seal furthercomprising means forming a fluid inlet and a fluid outlet for saidbuffer fluid compartment wherein said buffer fluid compartment surroundssaid annular flange, eccentrically thereof, whereby rotary movement ofsaid annular flange within said buffer fluid compartment duringoperation of the Rankine cycle system produces a pumping action fordrawing buffer fluid into said compartment through said inlet andexpelling buffer fluid from said compartment and through said outlet.

11. In a Rankine cycle system according to claim 10 a shaft seal furthercomprising:

a. means connecting said inlet and outlet means to form a closed loop inwhich said buffer fluid travels; and

b. reservoir means communicating with said closed loop for providing acontinuing supply of buffer fluid to replenish any buffer fluid whichpasses from said compartment into said working fluid chamber or saidenvironmental zone.

12. In a Rankine cycle system according to claim 11 a shaft sealwherein:

a. said reservoir means comprises a flexible, hermetically sealed bufferfluid confining means; and

b. said means constantly applying pressure applies pressure to saidflexible, hermetically sealed fluid confining means for exertingpressure on buffer fluid in said compartment.

13. In a Rankine cycle system according to claim a shaft seal whereinsaid means constantly applying pressure is responsive to the pressure insaid environmental zone and the pressure in said working fluid chamber.

14. In a Rankine cycle system according to claim 10 a shaft seal whereinsaid means constantly applying pressure comprises:

a. spring means for continuously applying pressure to said buffer fluidconfining means; and

b. means responsive to the pressure in said working fluid chamber andthe pressure in said environmental zone for applying to said bufferfluid confining means a pressure in addition to pressure applied theretoby said spring means, which at least substantially equals the higher ofthe pressures in the aforesaid zones,whereby the buffer fluid pressurein said compartment always exceeds both the pressure in said workingfluid chamber and the pressure in said zone of environmental pressure toprohibit passage of material along said shaft from said zone into saidworking fluid chamber or from said working fluid chamber into said zone.

15. In a Rankine cycle system according to claim 7 a shaft seal furthercomprising:

a. fluid conduit means having both inlet and outlet means connected tosaid buffer fluid compartment to form a closed loop; and

b. means forming a pump for causing fluid in said compartment to travelthrough said closed loop during rotation of said shaft.

16. In a Rankine cycle system according to claim 7,

a shaft seal wherein said pressure applying means comprises:

a. first means communicating with pressure external of said chamber;

b. second means communicating with pressure internal of said chamber;and

c. means responsive to said first and second communicating means forapplying to buffer fluid within said compartment a pressure at leastsubstantially equal to the greater of either said first or secondpressure levels.

17. In a Rankine cycle system including an expander casing means forminga chamber to contain fluid lubricant and organic Rankine cycle workingfluid, the interior and exterior of said chamber being characterized bydifferent pressure levels, and

rotary drive shaft means extending through said casing, a shaft sealcomprising:

a. first sealing means in fixed, fluid tight relationship to said shaftmeans and having a first surface portion and a second surface portion;

b. second sealing means in fixed, fluid tight relationship to saidexpander casing means and in sealing engagement with both said first andsecond surface portions of said first sealing means;

0. means forming a buffer fluid compartment in communication with saidfirst and second sealing means at their points of sealing engagement formaintaining a supply of buffer fluid at said points of engagement;

d. hermetically sealed compressible reservoir means in fluidcommunication with said compartment;

e. first means for continuously applying pressure to said reservoirmeans and thereby to buffer fluid within said compartment; and

f. second means for continuously applying pressure to said, reservoirmeans to thereby continuously pressurize buffer fluid within saidcompartment in addition to pressure applied thereto by said firstpressure applying means, the magnitude of which is functionally related.to the greater of either the pressure internal of said chamber or thepressure external of said chamber. 18. In a Rankine cycle systemaccording to claim 17 a shaft seal wherein said second pressure applyingmeans applies pressure to said buffer fluid which is at leastsubstantially as great as the greater of either the pressure within saidchamber or the pressure without said chamber, whereby the pressureapplied to said buffer fluid within said compartment is always greaterthan either the pressure within said chamber or the pressure withoutsaid chamber.

19. In a Rankine cycle system according to claim 18, a shaft sealwherein said compressible reservoir is for buffer fluid.

20. In a Rankine cycle system according to claim 19 a shaft seal furthercomprising means for indicating the amount of buffer fluid in saidreservoir.

21. In a Rankine cycle system according to claim 17,

a shaft seal wherein said second pressure applying means comprises:

a. first means communicating with pressure external of said chamber forapplying to said reservoir means a first pressure level having amagnitude substantially equal to said external pressure;

b. second means communicating with pressure internal of said chamber forapplying to said reservoir means a second pressure level having amagnitude substantially equal to said internal pressure; and

c. means associated with said reservoir means and responsive to saidfirst and second communicating means for applying to buffer fluid withinsaid compartment a pressure at least substantially equal to the greaterof either the pressure internal of said chamber or the pressure externalof said chamber.

22. A shaft seal interposed between relatively rotatable shaft means andeasing wall means through which said shaft means extends, said casingwall means having a first pressure zone on one side thereof and a secondpressure zone on the other side thereof, the pressure in said firstpressure zone being greater than the pressure in said second pressurezone under some conditions and less than the pressure in said secondzone under other conditions, said shaft seal comprising:

a. first sealing means mounted in :fixed relationship to said shaftmeans and forming first and second sealing surface areas eachsurrounding said shaft means;

d. means in hermetically sealed fluid communication with saidcompartment for continuously applying to buffer fluid within saidcompartment, under all conditions, a pressure which at leastsubstantially equals the greater of the pressures in said first andsecond pressure zones, thereby to inhibit passage of material along saidshaft means from either of said pressure zones to the other under allconditions.

1. A shaft seal interposed between relatively rotatable shaft means andcasing wall means through which said shaft means extends, said casingwall means having a first pressure zone on one side thereof and a secondpressure zone on the other side thereof, said shaft seal comprising: a.first sealing means mounted in fixed relationship to said shaft meansand forming first and second sealing surface areas each surrounding saidshaft means; b. second sealing means mounted in fixed relationship tosaid casing wall means and forming first and second sealing surfaceareas, said first and second surface areas formed by said second sealingmeans mating in sealing engagement with said first and second sealingsurface areas of said first sealing means, respectively; c. meansforming a buffer fluid compartment communicating with said first andsecond sealing means at their points of sealing engagement; d. firstmeans communicating with said first pressure zone; e. second meanscommunicating with said second pressure zone; and f. means responsive tosaid first and second communicating means for applying to buffer fluidwithin said compartment a pressure which at least substantially equalsthe greater of the pressures in said first and second pressure zones,thereby to inhibit passage of material along said shaft means fromeither of said pressure zones to the other.
 2. A shaft seal according toclaim 1 wherein said pressure applying means is responsive to thepressures in both said first and second pressure zones.
 3. A shaft sealaccording to claim 1 wherein said pressure applying means comprises: a.means forming a hermetically sealed expansible chamber communicatingwith said buffer fluid compartment; and b. means responsive to both thepressure in said first pressure zone and the pressure in said secondpressure zone for applying to said expansible chamber and thereby tosaid compartment a pressure at least substantially equaling the greaterof either the pressure in said first pressure zone or the pressure insaid second pressure zone.
 4. A shaft seal according to claim 3 whereinsaid pressure applying means further comprises means for constantlyapplying pressure to said expansible chamber and thereby to saidcompartment in addition to the pressure applied thereto by said meansresponsive to the pressures in said first and second pressure zones,whereby the pressure applied to said compartment exceeds the greater ofeither the pressure in said first pressure zone or the pressure in saidsecond pressure zone.
 5. A shaft seal according to claim 3 wherein saidexpansible chamber comprises a buffer fluid reservoir.
 6. A shaft sealaccording to claim 1 wherein said means responsive to said first andsecond communicating means is in hermetically sealed fluid connectionwith said buffer fluid compartment.
 7. In a Rankine cycle systemincluding an expander having means forming a working fluid chamber and arotary shaft extending from said working fluid chamber into anenvironmental zone, wherein the pressure in said working fluid chamberrises above environmental zone pressure during certain conditions anddrops below environmental zone pressure during certain other conditions,a shaft seal comprising: a. a first sealing means on said shaft infixed, fluid tight relationship thereto and having first and secondsealing surface areas surrounding said shaft; b. second sealing means infixed, fluid tight relationship to said means forming said working fluidchamber and having first and second sealing surface areas in sealingengagement with said first and second sealing surface areas,respectively, of said first sealing means; c. means forming a bufferfluid compartment in communication with said first and second sealingmeans at their points of engagement for maintaining a supply of bufferfluid at said points of engagement; and d. means in hermetically sealedfluId communication with said compartment constantly applying pressureto buffer fluid therein which at least equals the greater of either thepressure in said working fluid chamber or the pressure in saidenvironmental zone, said pressure being applied during both operatingand non-operating conditions of the Rankine cycle system, thereby toeliminate the tendency of material to pass along said shaft from saidworking fluid chamber into said environmental zone when pressure in saidworking fluid chamber is above environmental zone pressure and from saidenvironmental zone into said working fluid chamber when pressure in saidworking fluid chamber is below environmental zone pressure.
 8. In aRankine cycle system according to claim 7 a shaft seal wherein saidpressure applying means applies to buffer fluid within said compartmenta pressure greater than either the pressure of said working fluidchamber or the pressure of said environmental zone.
 9. In a Rankinecycle system according to claim 7 a shaft seal wherein: a. said firstsealing means comprises an annular flange surrounding said rotary shaft;b. said second sealing means comprises a pair of annular sealingsurfaces for sealing engagement with opposite sides of said annularflange; and c. said buffer fluid compartment surrounds said annularflange along and between the points of engagement of said annular flangewith said pair of annular sealing surfaces.
 10. In a Rankine cyclesystem according to claim 9 a shaft seal further comprising meansforming a fluid inlet and a fluid outlet for said buffer fluidcompartment wherein said buffer fluid compartment surrounds said annularflange, eccentrically thereof, whereby rotary movement of said annularflange within said buffer fluid compartment during operation of theRankine cycle system produces a pumping action for drawing buffer fluidinto said compartment through said inlet and expelling buffer fluid fromsaid compartment and through said outlet.
 11. In a Rankine cycle systemaccording to claim 10 a shaft seal further comprising: a. meansconnecting said inlet and outlet means to form a closed loop in whichsaid buffer fluid travels; and b. reservoir means communicating withsaid closed loop for providing a continuing supply of buffer fluid toreplenish any buffer fluid which passes from said compartment into saidworking fluid chamber or said environmental zone.
 12. In a Rankine cyclesystem according to claim 11 a shaft seal wherein: a. said reservoirmeans comprises a flexible, hermetically sealed buffer fluid confiningmeans; and b. said means constantly applying pressure applies pressureto said flexible, hermetically sealed fluid confining means for exertingpressure on buffer fluid in said compartment.
 13. In a Rankine cyclesystem according to claim 10 a shaft seal wherein said means constantlyapplying pressure is responsive to the pressure in said environmentalzone and the pressure in said working fluid chamber.
 14. In a Rankinecycle system according to claim 10 a shaft seal wherein said meansconstantly applying pressure comprises: a. spring means for continuouslyapplying pressure to said buffer fluid confining means; and b. meansresponsive to the pressure in said working fluid chamber and thepressure in said environmental zone for applying to said buffer fluidconfining means a pressure in addition to pressure applied thereto bysaid spring means, which at least substantially equals the higher of thepressures in the aforesaid zones,whereby the buffer fluid pressure insaid compartment always exceeds both the pressure in said working fluidchamber and the pressure in said zone of environmental pressure toprohibit passage of material along said shaft from said zone into saidworking fluid chamber or from said working fluid chamber into said zone.15. In a Rankine cycle system according to claim 7 a shaft seal furthercomprising: a. fluid conduit means having both inlet and outlet meansconnected to said buffer fluid compartment to form a closed loop; and b.means forming a pump for causing fluid in said compartment to travelthrough said closed loop during rotation of said shaft.
 16. In a Rankinecycle system according to claim 7, a shaft seal wherein said pressureapplying means comprises: a. first means communicating with pressureexternal of said chamber; b. second means communicating with pressureinternal of said chamber; and c. means responsive to said first andsecond communicating means for applying to buffer fluid within saidcompartment a pressure at least substantially equal to the greater ofeither said first or second pressure levels.
 17. In a Rankine cyclesystem including an expander casing means forming a chamber to containfluid lubricant and organic Rankine cycle working fluid, the interiorand exterior of said chamber being characterized by different pressurelevels, and rotary drive shaft means extending through said casing, ashaft seal comprising: a. first sealing means in fixed, fluid tightrelationship to said shaft means and having a first surface portion anda second surface portion; b. second sealing means in fixed, fluid tightrelationship to said expander casing means and in sealing engagementwith both said first and second surface portions of said first sealingmeans; c. means forming a buffer fluid compartment in communication withsaid first and second sealing means at their points of sealingengagement for maintaining a supply of buffer fluid at said points ofengagement; d. hermetically sealed compressible reservoir means in fluidcommunication with said compartment; e. first means for continuouslyapplying pressure to said reservoir means and thereby to buffer fluidwithin said compartment; and f. second means for continuously applyingpressure to said reservoir means to thereby continuously pressurizebuffer fluid within said compartment in addition to pressure appliedthereto by said first pressure applying means, the magnitude of which isfunctionally related to the greater of either the pressure internal ofsaid chamber or the pressure external of said chamber.
 18. In a Rankinecycle system according to claim 17 a shaft seal wherein said secondpressure applying means applies pressure to said buffer fluid which isat least substantially as great as the greater of either the pressurewithin said chamber or the pressure without said chamber, whereby thepressure applied to said buffer fluid within said compartment is alwaysgreater than either the pressure within said chamber or the pressurewithout said chamber.
 19. In a Rankine cycle system according to claim18, a shaft seal wherein said compressible reservoir is for bufferfluid.
 20. In a Rankine cycle system according to claim 19 a shaft sealfurther comprising means for indicating the amount of buffer fluid insaid reservoir.
 21. In a Rankine cycle system according to claim 17, ashaft seal wherein said second pressure applying means comprises: a.first means communicating with pressure external of said chamber forapplying to said reservoir means a first pressure level having amagnitude substantially equal to said external pressure; b. second meanscommunicating with pressure internal of said chamber for applying tosaid reservoir means a second pressure level having a magnitudesubstantially equal to said internal pressure; and c. means associatedwith said reservoir means and responsive to said first and secondcommunicating means for applying to buffer fluid within said compartmenta pressure at least substantially equal to the greater of either thepressure internal of said chamber or the pressure external of saidchamber.
 22. A shaft seal interposed between relatively rotatable shaftmeans and casing wall means through which said shaft means extends, saidcasing wall means having a first pressure zone on one side theReof and asecond pressure zone on the other side thereof, the pressure in saidfirst pressure zone being greater than the pressure in said secondpressure zone under some conditions and less than the pressure in saidsecond zone under other conditions, said shaft seal comprising: a. firstsealing means mounted in fixed relationship to said shaft means andforming first and second sealing surface areas each surrounding saidshaft means; b. second sealing means mounted in fixed relationship tosaid casing wall means and forming first and second sealing surfaceareas, said first and second surface areas formed by said second sealingmeans mating in sealing engagement with said first and second sealingsurface areas of said first sealing means, respectively; c. meansforming a buffer fluid compartment communicating with said first andsecond sealing means at their points of sealing engagement; and d. meansin hermetically sealed fluid communication with said compartment forcontinuously applying to buffer fluid within said compartment, under allconditions, a pressure which at least substantially equals the greaterof the pressures in said first and second pressure zones, thereby toinhibit passage of material along said shaft means from either of saidpressure zones to the other under all conditions.